Recently, measures have been taken to prevent falling of wall tiles from old buildings. In a method used for achieving such a purpose, for example, a hole is formed in a tile or tile joint to a depth reaching to a base concrete, and a resin is introduced through the hole so that the tile is fixed from the back.
In order to form a hole in a concrete, a hammer drill or vibrating drill which forms a hole in a drilled matter by rotating a super-hard drill so as to generate vibration or apply impact force is conventionally used. However, the drilling operation using a hammer drill or a vibration drill has a disadvantage in that a large mechanical sound is generated and vibration or noise associated with the operation is transmitted to the entire building. Thus, not only are the neighbors disturbed by the noise, but also falling of tiles is accelerated and the building may be further damaged.
In order to solve the above problems, a drilling tool of small diameter (3–15 mm) having a disc shaped bit at the tip of a rod-shaped or cylindrical shaft, and a drilling device, such as a handheld drill, including a rotation-driving device which rotates and drives the drilling tool around its axis may sometimes be used. As the bit of the drilling device, one in which super-grains are dispersed in a binder phase or one which is formed using a super-hard alloy is employed. Since the bit is rotated at a high-speed while it is pressed against a drilled matter so that a hole is formed with the generation of fine powder chips, the noise generated by the drilling device is less compared to that generated by a hammer drill or a vibration drill, and it becomes possible to carry out the drilling operation without causing vibration to the drilled matter.
In the above drilling device, although the chips are discharged by passing through a space between the surface of the wall being formed and the bit or the shaft, the fine powder chips tend to stay in the hole and are hardly removed as the depth of the hole increases. For a case where a liquid is introduced into the hole to facilitate the discharge of chips, it becomes difficult to smoothly supply and discharge the liquid for the same reason. If the chips remain at the bottom of the hole, the bit cannot reach the drilled matter and the drilling process cannot be performed. Also, when a hole is formed to a certain depth, no chips may be discharged and the bit cannot be advanced any further. Accordingly, it is difficult to form a deep hole of small diameter.
Moreover, the chips may stay not only at the tip of a blade (bottom of the hole) but also around the drilling tool (side surface of the hole), breaking the tool and decreasing the number of rations thereof. This causes a decrease in drilling efficiency, and there is a danger that heat may be generated and a brazed chip may fall.
In order to smoothly discharge the chips at the drilling position, if a shaft is made hollow and a core bit which drills while forming a core center in the hole is used, it becomes possible to decrease the amount of chips generated. Also, it becomes possible to discharge the chips by introducing a fluid, such as water and a gas, from the outside to the drilling position through the hole.
However, in a conventional wet process in which chips are discharged by supplying water, the operation place may be swamped by the water or the dirty water containing fine power chips may be spattered, contaminating the surrounding environment. Thus, a cleaning device may be needed in addition to the drilling device, and hence the use of the conventional process is not preferable.
Also, as for the above-mentioned drilling tool of a small diameter of 3–15 mm, for example, a large amount of chips is generated relative to a hole of small diameter since a core bit cannot be employed with the drilling tool. Also, since the fluid used for discharging the chips can be supplied only through an opening of the drilled hole, it is extremely difficult to discharge the chips generated.
That is, in the conventional drilling device, it is difficult to form a deep hole of small diameter, and not only is the drilling efficiency reduced as the depth of the hole increases, but also a hole having a desired depth may not be formed, depending on the diameter of the hole. Furthermore, since the above drilling device requires not only the drilling tool and the rotation-driving device but also a device for supplying fluid, such as a compressor, there is a problem in that the scale of the overall device is large.